There is an occasion to extract a nucleus area from a cell image. Specifically, it is important to efficiently recognize a nucleus area from the obtained image in order to construct the cell lineage of the nematode. The so-called Nomarski microscope is used to obtain a cell image. According to the Nomarski microscope, the external shape and distribution of contents of a transparent subject are observed as light and dark images. Biologically, a cell content (nucleus) and an external shape (cell membrane), both transparent when using a common optical microscope, can be observed as images of light and dark.
Conventionally, a plurality of image processing algorithms are used for extracting a nucleus area from an image taken by the Nomarski microscope. These image processing algorithms comprise an approach for detecting an area, where the fine brightness variation in the image is poor, as the nucleus, or an approach for extracting a portion, in which the change in the intensity is large in a wide range along the incident angle of the light, as the nucleus. The former is exemplified by using a filter obtained by a combination of a Kirsch template type edge detection operator with a moving average, or a filter binarizing the output of a Prewitt template type edge detection operator and applying a distance transform. For the latter, a filter for taking a difference in a sum of intensity value of a predetermined top and bottom pixel along a seeming angle of light is adopted.
However, the nucleus detection by these image processing algorithms is not perfect, and therefore, an area recognized by any one of three types of algorithms is determined as a nucleus area as a conclusion of a whole image processing system, which results in a complicated nucleus extraction operation.
In a cell image taken by the Nomarski microscope, a cytoplasmic portion is coarse in image quality, while a nucleus area is relatively smooth in image quality. A method for extracting a smooth area as a nucleus from an image is studied using differences in image quality.
An object of the present invention is to efficiently extract a smooth or coarse portion in image quality from an image.
Another object of the present invention is to provide a filter that is capable of extracting a smooth or coarse portion in image quality from an image.